Furnace



J. FREI, JR

Qct. l0, 1950 FURNACE Filed April 25, 1947 Patented ct. 10,

2,525,407 INJRNACE John Frei, Jr., Chicago, Ill. Application April 25,1947, serial No. 143,145

3 Claims.

My invention relates to a furnace and to Va method of heat treatingarticles and particularly to a furnace for and method of continuouslyheat treating molds for casting.

Although my invention may be used advanta-l geously for the heat'treatment of many types of articles, it is particularly Well adaptedfor continuous heating of flasks which contain molds, such as are usedin centrifugal casting operations, and the invention will therefore bedescribed in that connection. The flasks contain mold formn ing materialof silica in finely divided form which surrounds a Wax or plasticpattern corresponding in shape to the object to be cast. When thepattern is removed from the mold by being melted and burned out, thespace which it occupied constitutes the mold cavity into which moltenmetal will be cast.

It is highly important that during the melting and burning out of thewax or plastic patterns that none of the particles of the nely dividedmold-forming material detach themselves from the surface of the moldcavity, otherwise the mold cavity Would be imperfect in shape and causean imperfection in the casting. It is an object of my invention toprovide adequate heating of a mold While supporting it substantiallyfree of vibrations whereby the pattern may be burned out without causingparticles of the mold forming material to become detached from thesurface of the mold cavity. In accomplishing this object I provide aplatform for the flasks which contain the molds to be heated, whichplatform is supported by a float which is carried on a body of liquid.In this Way vibrations received by the furnace or its supportingstructure are not transmitted in any substantial degree to the platformwhich carries the fiasks and their molds.

It is a further object of my invention to produce molds which not onlyhave the pattern of the mold completely burned out without damage to themold cavity but which also are heated to the temperature desired, insome cases to a temperature approximating that of the molten metal whichwill be delivered to it in the casting operation.

So that continuous casting may be performed by centrifugal castingmachines, it is a further object of my invention to provide a furnacewhich is adapted to heat a series of flasks in sequence so that aproperly heated mold with the pattern burned out will be ready each timethe molten metal to be cast is at the proper temperature in the Crucibleof a centrifugal casting machine such as that illustrated inmy copendingappli-A 2 cation, Serial No. 751,655, filed June 2, 1947. In this Way aflask containing a properly heated mold may be removed from the furnaceand immediately transferred to the casting machine and the molten metalcast with a minimum of delay. There is therefore a minimum loss of heatin the mold and a minimum loss of heat from the crucibleeontaining themetal to be cast. Consequently chilling of the metal in the Crucible andalso as it is being cast in the mold is eliminated.

In the accomplishment of the foregoing object I provide an additionaladvantage in that the furnace of my invention provides a rotatableannular Work supporting platform and a single entrance or loadingstation for the platform such that fresh flasks may be positioned on theplatform as heated nasks are removed therefrom to go to the centrifugalcastingv'machine.- This arrangement provides convenience and economy inoperation since only a single operator is required for loading andunloading the platform. Since the platform is annular, the furnace iscompact and does not have to extend longitudinally over al great extentof floor space. to the platform as being annular in shape it will beunderstood that any platform Vsubstantially circular in outline may beemployed and constitutes an equivalent structure. tangular platformcould be employed, but it would not be practical.

It is a further object ofv my invention to provide a self-balancingmechanism for the annular float-supported platform o f my furnace sothat as fiasks or other objects are initially placed on the Worksupporting platform and thereby form an unbalanced load on it, theplatform will be maintained substantially horizontal so that the flasksWill not tip over or slide from the platform.A

It is still another object of my invention lto provide in the heatingchamber of my furnace means for causing a now of heat from that zone ofthe chamber where the heating means is located toward the entrance ofthe chamber Where the objects to be heated are introduced to the`chamber. This construction is provided so that as the movable platformcarries the objects .to be heated toward the zone where the maximum demsired temperature is imparted to them, they pass Although I refer Even arecnumeral ID indicates the furnace generally. To

the center of the base I2 of furnace I there is secured a verticallyextending vpost or pillar I4 which supports cross bars, such as the barsI6,`

at its upper end. The outer framework, indicated generally by thereference numeral I8, comprises a series of vertically extending postsor angle irons, such as the posts which interconnect the base I2 withthe cross bars I6. At an intermediate point on the center post I4 thereis positioned a xed bracket 22 which carries a supporting platform 24.At a corresponding height on the posts 201 of the outer framework I8there .is supported an annular platform 26 which is spaced from theplatform 24 in such fashion as to provide an annular slot 28 for apurpose to be described hereinafter.

A heating chamber or oven, indicated generally by the reference numeral30 is annular in form and is constructed of re brick or other heatresistant material. The base 32 of the heating chamber 30 is supportedon the platforms 24 and 26, and side walls 34 and 36 in lturn areAsupported on the base 32. A top wall 38 bridges the side walls 34 and 36to completethe chamber.A An entrance 40 (see Figure 2) to the chamber361 is provided by an opening in the outer side Wall 34.

The heating chamber 30 may be heated by any one of a number of wellknown heat supply-V ing means. but it will be appreciated that it may beoil fired orelectrically heated if desired. Gas supply pipes 42 from agas source (not shown) have their burners or jets 43 located adjacentapertures 44 and 46 in the side walls 34 and 36, re'- spectively, of theoven 30. As may be seen in Figures 1 and 2 the apertures flare inwardlyto accommodate the flame which issues from the burners 43 when they arelit. The gas burners 43, generally referred to as the heat supplyingmeans, extend only part way about the annular heating chamber and, aswill be noted from Figure 2, extend inwardly of the chamber 30 from oneside of the entrance 46'.

A door 48 of fire resistant material is adapted v,

to close off the entrance 4I! from that zone of the heating chamber 30which contains the heat supplying means. The door 48 has secured to ita. Wire cable which passes over a -pair of pulley wheels 52 and 54 andhas secured at its other end a counterweight 56 which is guided in avertically extending tube 58. By means of the counterweight y56 andcable 50, the door 48 may be easily raised or lowered with little effortby the operator who is standing adjacent the entrance 40.

Within the heating chamber 30 of furnace I0, there is an annular movableplatform indicated generally by the reference numeral Elli. The articlesto be heated, such as flasks 62, are placed on the platform 60 formovement through the heating chamber 30. Vertically extending flanges orridges 64 may be formed on the top surface of platform 60 for supportingthe flasks 62 and for permitting an openspace beneath thev The furnaceillustrated is gas red, .1.,

-3 to the plate 'I6 about the aperture 18.

li flasks so that the pattern, when melted, may run out or readilyvaporize. It will be understood that the flasks are placed in invertedposition upon the platform 60, that is, with the pouring sprue of themold pointed downwardly so that the pattern, when melted, may flowdownwardly on to the platform 60 between the ridges 64. Instead offlanges or ridges 64, temporary, removable supports, such as a pair offlre bricks, providing an opening beneath. the mold cavity of the flasksmay be employed. Platform 60 is supported by means of a hollow float 66formed of sheet metal. The float may, of course, be

Yformed of wood or other material which will float in the liquid 6Bwhich supports it. The liquid is carried in an annular sheet metal tank10. Tank 'I6 is positioned on the base I2 of furnace II) and is axiallyaligned with the annular heating chamber 30. Float 66 is interconnectedwith the supporting platform 66 by means of a plurality of verticallyextending rods '12. The float is movable within the annular tank Ill andin order to guide it so that the vertically extending rods 12 connectedto it do not touch either of the side walls of the heating chamber 30which define the annular slot 28 through the rods 'i2 extend, guidemeans, indicated generally by the reference numeral 74, is provided.

The guide means 'I4 comprises a plate 16 having a plurality of apertures'i8 (see Figure 3) spaced about its margin so that the vertical rods 'I2may pass therethrough without ever touching the plate. Plate 'I6 iscarried for rotation about the central post I4 by a roller bearingassembly, indicated generally by the reference numeral 86, which iscarried by the central post I4. Plate 'I6 is not movable axially. Aflange 82 secured to the lower end of each rod 'I2 is adapted to seatupon and connect with the top of the float 66 in a recess. By reason ofthe collar 84 on the flange 82 a spring 86 is adapted to seat on theflange but be maintained out of contact with the rod 12. The upper endof spring 86 engages about a collar 88 of a flange 981 which is securedIn this way the platform 66 is supported upon a float 66, which floathas connection with the plate 76 through the medium of a plurality ofsprings 86. Consequently the vibrations from the ground or base of thefurnace will be substantiallyeliminated by the liquid 68 in the tank 10and will not be transmitted to the platform 66. Also, vibrationstransmitted to the plate16 will be substantially eliminated by reason ofthe resilient connection between plate 'I6 and the float 66 by reason ofthe springs 86. Consequently plate 'I6 may guide the supporting platforml6I)V in its rotation within the chamber 3c without transmittingvibrations thereto and may thereby prevent the float 66 and platform 66fromfioating laterally into contact with the side walls of the tank 'I8or of the annular slot 28, respectively.

The guiding mechanism 'I4 serves an additional purpose in that it servesto maintain the movable platform 6l) in substantially horizonta1position even when an unbalanced load is placed thereon. During theinitial loading of platform 60 with the flasks 62, one side of theplatform becomes heavier than the other and the float t6 therefore has atendency to sink downwardly" each of the springs-seat against, theplateV "I6,V

which is` held against axial movement onv central post I4, the springs8E resist upward movement of the float and therefore serve to maintainthe floats balance with the result that the platform 6i! continues toremain in a substantially hori- Zontal plane. This balancing mechanism,however, transmits substantially no vibration to the platform 6D as wasexplained above.

Horizontal frame members IB. and 92, which are carried at the upper end'of central post I4, serve to' brace andV support a hood, indicatedgenerally by the reference numeral gli, for the. furnace IB.. A flueSfor the hood 94 carries off heat which is escaping from the surface ofthe heating chamber til. The hood and flue may be formed of sheet metalor other suitable material and the hood may extend downwardly along theside of the furnace It, as shown.

Since the wax orplastio patterns are melted or burned out of the molds,various gases and solids willbe, produced which needto be carried onfrom the heating chamber or oven St. For this purpose aflueil,connecting at its upper end to the ue 95 of hood 94, is provided overthe opening itil in the upper Wall 38v of the heating chamber 3Q'. Inaddition to carryingoff waste gases, the flue Se, servesanothervaluablepurpose in that it draws heated air andA gases fromLthat zone of theheating chamber whereV the gas burners are situated around towardtheentrance 40 of the chamber Si?, so that the iiaskswhich are moving fromthe entrance in the direction of the arrow A of Figure 2 toward theburners, will be passing through a zone which is increasing intemperature. Consequently, the. temperature molds is increased graduallyand not suddenly. In the preferred form of my invention the flue islocated as shown in the drawings, which position corresponds to that atwhich the patterns in the mold begin to burn. The temperature at thislocation is approximately 400 F. It will be understood, however, thatthe flue may be positioned closer to the entrance d so that the hotgases and air from the zone which is being heated directly by the gasburners will be drawn around even farther in the chamber to spread outthe zone of gradually increasing temperatures through which the askstravel.

In the operation of my furnace, the gas burners e3 are lit and theoperator then begins to load the platform Si) through the entrance 4U.The flasks i5?. are spaced from each other and as the available portionof platform Bil is covered, it is rotated in the direction of the arrowA of Figure 2 to provide supporting surface on the platform Bil which isyet unfilled. When the molds are being prepared for the casting ofnon-ferrous metals, the door 48 may be left open, that is, in its raisedposition while the gas burners are operating. However, if ferrous metalswill ultimately be poured into the molds in the flasks 62, the door islowered so that it is in closed position. A- though the platform 6B isgenerally rotated by hand, it is contemplated that it may be motordriven through the plate 16 and springs 86 or by other means. Anyunbalanced load which is placed on platform 60 during the initialloading thereof is counteracted by the springs 8S and plate 76 whichoperate to maintain the float 65 in substantially the same horizontalplane. As each of the flasks on the platform approaches a positionbeneath the flue 98, the wax or plastic pattern within the mold hasreached a tempera- -ture at which it begins to melt, and then burn.v

The Waste gases or combustion are drawn up the of the 6 flue 9S.Simultaneously, heated air and other" gases from the zone of the heatingchamber 3B which has the gas burners it is drawn in a direction oppositeto that indicated by the arrow A in Figure 2', toward the fiue andtoward the as'ks which are approaching the Zone which is heated directlyby the gas burners. causes the flasks, molds and.'A patterns within themolds to be heated gradually while the patterns are being burned out.-When the flasks ultimately reach the zone of the heating chamber 3i!whichhas the gas burners 4.3,. where the temperaturev may be i800o F. orhigher, the flasks are heated. tol their desired maximum. temperature;Such temperature may approximate that of the metal which will be castinto. the molds so that the metal will not be too quickly chilled duringthe casting operation.

As' theplatform becomes. fully loaded and theinitia-l flasks-placed.thereon approach the' entrancedafter passing through thezone of maxi'-mum temperature, the operator will raise the door 158', rotate theplatform, lower the door LEB' and rem-ove a flask 62. A fresh ask 62 isthen placed upon the platform where the heated one: wasv removed and thedoor 48 is again raised andv the platform rotated in thedirection ofthearrow A to thereby deliver to the entrance 40 another heated flask 52'.It will be appreciated'that by a suitable camming arrangement or othermeans, the rotation of the platformv B could automatically cause araising and lowering of the door 48 to permit the passage of heatedflasks beneath the door to the entrancerllli. It will be seen that Iprovide continuous heat treatment of flasks, which continuous treatmentis very advantageous When casting operations aracarried out by cen`trifugal casting machines at a rapid rate. My furnace provides heatedflasks at the proper temperature and proper time for positioning in acentrifugal casting machine with a minimum loss of heat from the flasksand a minimum loss of heat from metal in the crucible of the castingmachine. Coordination of the timing of operations between the castingmachine and the furnace may be provided so that the rate of delivery ofthe furnace corresponds to the rate of casting in a centrifugal castingmachine.

Any vibrations which, during the burning out of the patterns, would tendto dislodge particles of the mold forming material from the sides of thecasting cavity are eliminated by supporting the platform by means of theiloat 66 in a body of liquid B8. Furthermore the mechanism formaintaining the platform balanced is so constructed as to eliminatesubstantially all vibrations from being transmitted through it to theplatform 68. Said balancing mechanism also serves to guide the platform60 and float 6B in their associated movements to prevent their contactwith the walls of the heating chamber 3U and the walls of the tank lil,respectively. Since my furnace may be operated continuously and sincethe temperature therein may be maintained at the desired degree at alltimes, it will be seen that great savings in time are provided ascontrasted with operations in the standard furnace wherein asks arepositioned, heated and withdrawn and the 'furnace then permitted to cooldown before being loaded again with another batch of flasks.

Although I have described and illustrated a preferred embodiment of myinvention, I do not intend to be limited thereto except in so far as ythe appended claims are so limited, since my dis- 7 closure will suggestto those skilled in the art certain modifications and changes.

I claim:

1. In a furnace having Walls defining a chamber, an entrance to saidchamber, an opening in a wall of said chamber and means for supplyingheat to the chamber, the combination of a rotatable work supportingplatform; means for supporting the platform including a movable float,liquid for carrying the fioat, and supporting elements interposedbetween the platform and the float and adapted to extend through saidopening in a wall of the chamber; a xed support, a resistor memberrotatably carried by said xed support and resiliently engaging the floatfor the platform and acting to maintain the float bafanced whenunbalanced loads are applied to the platform.

2. A furnace comprising, in combination, wall means defining a heatingchamber, means for supplying heat to said chamber, an entrance to saidchamber, a movable work supporting platform within said chamber,floating means for buoyantly supporting the platform, means acting tomaintain the ioating means balanced when unbalanced loads are applied tothe platform, said balancing means comprising a resistor member andresilient means interposed between the resistor member and the floatingmeans.

3. A furnace comprising, in combination, wall means defining a heatingchamber, means for supplying heat to said chamber, an entrance to saidchamber, a work supporting platform movable within said chamber,floating means for buoyantly supporting the platform, said floatingmeans including a liquid-containing-tank and a float disposed thereinbeneath said platform and 8 supporting elements interposed between theplat` form and float, and means for guiding the platform for movementand for acting to maintain the fioating means balanced when unbalancedloads are applied to the platform, said guiding and balancing meanscomprising an apertured rotatable plate fixed against axial movement anda plurality of resilient elements interconnecting the rotatable plateand the oat, each of said supporting elements extending through, andbeing out of contact with, an aperture in said plate and a resilientmember.

JOHN FREI, JR.

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